Electron cooling

Electron cooler (left in the picture) in the Low Energy Ion Ring (LEIR) at CERN . The electron source and electron collector are located in the silver cylinders at the top

The electron cooling is a method to direct a beam in a particle accelerator by means of an electron beam to cool d. H. to reduce the size of the particle packets in phase space or the emittance . The mass of the particles in the beam to be cooled must be greater than the mass of the electrons.

history

In 1966 Gersch Izkowitsch Budker proposed electron cooling as a method for damping oscillations of a proton beam in a storage ring . Electron cooling was demonstrated for the first time in 1974 at the "NAP-M" storage ring in the Budker Institute for Nuclear Physics (BINP) in Akademgorodok . The first system was built at CERN in 1977. Nowadays, electron cooling is used in many synchrotron particle accelerators and storage rings.

functionality

An electron beam is generated with an electron source. This beam is accelerated by a static electric field . In the potential of the accelerating electric field, all electrons are accelerated by the same amount regardless of their exact path. This means that the speed distribution of the electrons is very narrow. The electron beam is accelerated to such an extent that the speed of its electrons corresponds to the mean speed of the particles in the particle beam.

After the acceleration, the electron beam is superimposed with the particle beam with the aid of magnetic fields. In a straight flight path, particles that do not swim with the electron flow often hit the electrons. These impacts generate impulses for the electrons and thus cool the beam. After a few meters of common flight, the electrons are decoupled and caught.

The particle beam to be cooled can only be cooled down by means of electron cooling until it is in thermal equilibrium with the electron beam.

The energy to accelerate electrons of mass to the same speed as particles of mass and energy is . ${\displaystyle m_{e}}$ ${\displaystyle m_{p}}$ ${\displaystyle E_{p}}$ ${\displaystyle E_{e}={\frac {m_{e}}{m_{p}}}E_{p}}$

use

Electron cooling is an important aid in the generation of antimatter, so at the Antiproton Decelerator at CERN, electron cooling offers a higher cooling rate than stochastic cooling .

The use in pre-accelerators is also widespread, for example lead ions are provided for the Large Hadron Collider (LHC) in the Low Energy Ion Ring (LEIR) .

Electron cooling is also used to improve beam quality, for example on the COZY cooler synchrotron .

The use of electron cooling is restricted by the energy required to accelerate the electrons. In previous electron cooler systems, electron energies of up to a maximum of 300  keV were common, corresponding to a proton energy of 550 MeV. Stochastic cooling was therefore used at higher speeds.

The largest facility is located at the Fermi National Accelerator Laboratory . Since mid-July 2005, antiprotons with an energy of up to 8 GeV have been cooled by electrons with a maximum electron energy of 4.3 MeV on a 20 m long cooling section . A current of up to 0.5 A flows during operation.

See also

• Stochastic cooling
• Beam temperature

Web links

• Electron Cooling Mission. Fermi National Accelerator Laboratory , February 17, 2011, archived from the original on October 15, 2011 ; accessed on July 6, 2016 (English, no longer active website of the project). 
• Babatunde O'Sheg Oshinowo, Jerry Leibfritz: Survey and Alignment of the Fermilab Electron Cooling System. 9th International Workshop on Accelerator Alignment, September 26, 2006, accessed July 6, 2016 . 

Individual evidence

1. ^ GI Budker: An effective method of damping particle oscillations in proton and antiproton storage rings . In: Atomic Energy . 22, No. 5, 1967, pp. 438-440. doi : 10.1007 / BF01175204 .
2. ^ GI Budker et al .: Experimental Studies of Electron Cooling . In: PAAC . 7, 1976, p. 197.
3. ↑ ^{a b} Sergei Nagaitsev: Electron cooling demonstration with Recycler 8.9-GeV / c pbars. (pdf; 254 kB) Fermi National Accelerator Laboratory, July 18, 2005, accessed on January 19, 2011 (English, presentation slides). 
4. ↑ ^{a b} Gerard Tranquille: ICE-cool beams just keep on going. CERN Courier, August 25, 2009, accessed December 30, 2009 . 
5. ↑ Frank Hinterberger: Physics of the particle accelerator and ion optics . 2nd Edition. Springer Verlag, Berlin 2008, ISBN 978-3-540-75281-3 , p. 359 , doi : 10.1007 / 978-3-540-75282-0 .